Permit vs no permit on interior construction

[Ralph Ace]

I showed a home and asked the listing agent why the home went contingent and then got relisted.

The agent said the inspection went bad because there was no permits on any work done.

The home had fully remodeled kitchen, bathrooms, flooring, etc.

The listing agent said the contractor has done everything to code and has years of experience.

Do you need permits on everything done inside the home and will inspection fail with no permits.

Can anyone provide any feedback on this topic.